Plasticizing elastomers



Patented Jan. 10, 1950 UNITED STATES PATENT OFFICE PLASTICIZING ELAS'IOMEBS John Richard Vincent, Newport, DeL, asslgnor to p E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application October 5, 1946.

Serial No. 701,395

9 Claims. (01. 280-323) 1 2 This invention relates to the plasticizing of Example 1 elastomers, and more particularly to an improved process for increasing the plasticity of elastomers by intimately incorporating therein an anilide of a beta-keto acid. 1

It is well known that, in the working of natural rubber and synthetic rubbers, the material in the unvulcanized state is' generally tough and hard and requires considerable working or chemical treatment to make it sufliciently plastic for proper processing. Usually, chemical plasticizers are incorporated in such elastomers in the unvulcanized state to give them improved working properties. These plasticizers are usually sulfur compounds or sulfur-containing materials such as mercaptans, thioacids, thiurams, etc. These sulfur-containing plasticizers, when incorporated in the elastomers, offer certain disadvantages in the subsequent use of the elastomers, particularly with regard to the tarnishing of metals such as silver, etc., and, in some cases, there are indications which lead to the belief that certain of these plasticizers contribute to the instability of the I have found that elastomers which are polymers of 1,3-diene compounds or copolymers thereof with mono-olefinic compounds may be plasticized by intimately incorporating therein from 0.1% to 5.0%, based on the weight of the elastomer, of an anilide of a beta-keto acid. These plasticizing agents may be incorporated in the elastomer by working on the usual rubber mill or in an internal mixer at temperatures of from 30 to 160 C., or they may be added'to the elastomer latex before coagulation. The anilides of the beta-keto acids are particularly suitable for plasticizing natural rubber and the rubber-like butadiene-styrene interpolymers, butadiene-acrylonitrile interpolymers, chloroprene (2-chloro-1,3-

butadiene) polymers and chloroprene interpolymers which are illustrative of the type of elastomers referred to by Fisher as elastoprenes in his suggested nomenclature of rubber-like materials found inthe Jr. of Ind. 8: Eng. Chem., ,vol. 31,

No. 8 of August 19, 1939, pages 941-945. In gen- 55 Chloroprene was polymerized in an emulsion, using the following recipe:

alkaline Daxad-ll is the sodium salt of the condensation product of naphthalene sulfonic acid and formaldehyde.

- The sulfur, rosin and stearic acid were dissolved in the chloroprene, which was then emulsified in the water containing the other ingredients.

The polymerization was carried out at C. with agitation and continued until the specific gravity of the polymer emulsion reached a value of 1.068. The polymerization was then stabilized by the addition of varying amounts of the plasticizers listed in the following table, which, when added to the polymerization mass, stop the polymerization, and, after acidifying to litmus with a 10% solution of acetic acid, was coagulated with brine. The plasticity and recovery numbers (Williams Parallel Plate plastometer-high plasticity numbers mean low plasticity) of polymers stabilized with different materials is tabulated below.

Plasticizer Plasticity Recovery Nona 242 157 1 part Aeetoacetanilido 131 120 2 parts Aoetoacetanilide 116 94 2 parts Tctraethyl thiuram disulflde 154 58 2 parts Tetraethyl thiuram disulflde+2 parts Aoetoacetunilide Too soft-to handle.

anilide, incorporated into a polymer before coagulation, causes that polymer to have a higher plasticity and a lower recovery than a similar polymer obtained in the absence of acetoacetanilide.

Polymers obtained in the absence oi acetoacetanilide can be plasticized by incorporating acetoacetanilide into the dry polymer, as illustrated in the following exam les.

Example 2 Samples of the variou elastomers identified in the following tables were milled, with and without 2% of acetoacetanilide, based on the weight oi elastomer, as the plasticizer, on a C. rubber mill. After 3 minutes, two plasticity pellets were cut from the sample-and milling continued for2 minutes longer. Then two more pellets were cut,

etc., for the various periods of milling indicated in the tables. (Each value is the average of two determinations.) The various elastomers employed in these tests are products of commerce Milling Time "a car 011- lutlolser None I 2% Recov. Plast. Recov.

which may be particularly characterized as follows:

GR-M-A sulfur modified chloroprene polymer. 1

GR-M GR-M-IO Plesticlur Plasticlzer Mum None 2% None 2% Plant Recov. Pleat. Recov. Plast. Recov. Pleat." Recpv.

(111-8 13. car OR-lfi Plasticixer lasticizer Mining Time None 2% None 2% Plast Recov. Pleat. Reoov. Plast. Recov. Plast. Recov.

mo 205 150 no 190 189 136 142 143 145 180 195 1 195 130 143 131 133 134 192 128 125 138 107 127 102 196 115 166 130 Merceptan Modified Ohloro- P-840 l rene Pol er I Plastlcixer P Milling Time None 2% None 2% Float Reoov. Pleat. Reeov. Plast. Recov. Plast. Recov.

112 1s 9s 2 11s 10 1 111 10 102 4 20 l 104 4 101 3 A polymer made as described in Example 1 except that the sulfur was replaced with 0.25 part of iodoi'orm.

1 The mercaptanmodified chloroprene polymer was produced by the process more partlculary described in Example 1, with the following changes: The sulfur was Only 0.16 part oi'KzSzOs was used. Resin pa or sodium anthraqnibeta-sulfonate was added and the polymerization was stopped at approximately Example 3 Certain of the runs of Example 2 were repeated unmodified chlor '5) was worked,

These experiments show that acetoacetanilide a plasticizer at temperatures as low as 50 and as high as 121 15 ried out in an internal mixer in place 01' a mill.

' as illustratedinExamplei.

C.- C. The mixing may be car- Example 4 Using a laboratory W. 81?. mixer heated with 20 steam under apressure 0123 p. s. i., 50 g. of an oprene polymer (see Example I with and without the presence of acetoacetanilide, for 10 minutes. After this treatment, the two samples were examined on a rubber mill. The sample worked in the presence of the acetoacetanilide had better milling characteristics than the sample worked in its absence.

' Example 5 Acetoacetanilide will increase the plasticity of a very tough variety of neoprene (made as in Example 1, omitting the sulfur and stabilizing with 0. 5 part of NaHSOa, 0.5 part of tetraethyl thiuram disulfide and 0.5 part of monobenzyl ether of hydroquinone). This polymer (500 gr.) was milled on a 12 inch, 121 C. mill for 4.5 minutes at 0.03 inch gauge, then for 1.0 minute at 0.02 inch gauge and then for 4.5 minutes at 0.015 inch gauge. The mill was cooled to 50 C. and the sample was milled for 5 minutes. The plasticity of the sample, without a plasticizer, was 348.

The procedure was repeated, using 500 g. of the polymer and g. of acetoacetanllide. The plasticity of this sample was 264.

Example 6 Other anilides of acetoacetic acid also are plasticizers, as shown in the following table, where each compound was tested at 2% based on the amount of the same polymer' used in Example 5. These tests were made by milling the elastomer for 10 minutes on a 125 C. rubber mill.

Compound Added Plasticity Recovery None 345 175 Acetoacet-o-toluide 280 140 Acetoacet-mcyanoanilide 260 142 .Acetoacet-p cbloro-o-phenetidide. 268 137 Acetoacet-pchloro-o-aniside 250 135 It is very unusual to find materials which peptize an unmodified chloroprene polymer, as it has been generally recognized that such polymers are impossible or, at best, very dimcult to soften.

The anilides of the beta-keto acids, which may be employed in place of those specifically designated above, are those having the formula:

(hm-C 0011 0 ONE-Cum Benzoylacetanilide Cam-C O 011:0 ONE-0J1; Beta-naphtboyl acetanilide C Hu-C 0 CHQC ONE-Cd! Hexabydrobenzoyl acetanilide (CH0 :0 03:0 0 CHgC ONE-Can; Tert-hexoyl acetanilide This invention provides a means of increasing the plasticity and processability of 'elastomers with agents containing no sulfur, thus eliminating any instability that might be caused by sulfur compounds. It makes possible the use oi some polymers in contact with metals, such as silver, without tarnishing the metal, as would occur if a sulfur-bearing material were present.-

I claim:

1. The process of increasing the plasticity of an elastoprene of the class consisting of natural rubber and the polymers of 1,3-butadiene and of 2-chloro-1,3-butadiene which contain at least 50% of the 1,3-butadiene compound, which comprises intimately incorporating in such material in the unvulcanized form from 0.1% to 5.0% of an anilide of a beta-keto acid of the formula R--CO-CH-. -CONHR', wherein R stands for a radical of the group consisting of phenyl and naphthyl radicals and alkyl radicals of from 1 to 6 carbon atoms, and R stands for a radical of the group consisting of phenyl and naphthyl radicals.

2. The process of increasing the plasticity oi. an elastoprene of the class consisting oi! natural rubber and the polymers of 1,3-butadiene and of 2-chloro-1,3-butadiene which contain at least 50% of the 1,3-butadiene compound, which com-- prises intimately incorporating in such material in the unvulcanized form from 0.1% to 5.0% of acetoacetanilide.

3. The process of increasing the plasticity of rubber which comprises intimately incorporating therein from 0.1% to 5.0% of acetoacetanilide.

4. The process of increasing the plasticity oi a chloroprene polymer which comprises intimately incorporating therein from 0.1% to 5.0% of acetoacetanilide.

5. An elastoprene of the class consisting of natural rubber and the polymers of 1,3-butadiene and of 2-chloro-1,3-butadiene which contain at least 50% of the 1,3-butadiene compound containing from 0.1% to 5.0% of an anilide of a beta-keto acid of the formula R--COCH2CO-NHR', wherein R stands for a radical oi. the group consisting of phenyl and naphthyl radicals and alkyl radicals of from 1 to 6 carbon atoms, and R.

stands fora radical of the group consisting of phenyl and naphthyl radicals.

6. An elastoprene of the class consisting of natural rubber and the polymers of 1,3-butadiene and of 2-chloro-1,3-butadiene which contain at least 50% of the 1,3-butadiene compound containing from 0.1% to 5.0% of acetoacetanilide.

'7. An unvulcanized elastoprene of the class consisting of natural ,rubber and the polymers of 1,3-butadiene and of 2-ch1oro-1,3-butadiene which contain at least 50% of the 1;3-butadiene compound of improved plasticity containing from 0.1% to 5.0% of an anilide of a beta-keto acid of the formula RCOCHa-CONI-IR', wherein R stands for a radicalof the group consisting of phenyl and naphthyl radicals and alky1 radicals of from 1 to 6 carbon atoms, and R stands for a radical of the group consisting of phenyl and naphthyl radicals.

8. An unvulcanized chloroprene Polymer of improved plasticity containing from 0.1% to 5.0% of an anilide of a beta-keto acid of the formula R-COCH2-CO-NHR', wherein R stands for a radical of the group consisting of phenyl and naphthyl radicals and alkyl radicals of from 1 to 6 carbon atoms, and R stands for a radical of the 9. An unvulcanized chloroprene polymer 01 improved plasticity containing from 0.1% to 5.0%

8 v UNITED STATES PATENTB or acetoacetanllide;

\ Name Date 2s 'hrodam Aug. 7, 194; JOHN RICHARD 2.415.350 Kello g Feb. 4, 1941 REFERENCES CITED OTHER. REFERENCES The following references are of record in the lniandlim. Chemistry, me of this patent; 941 045, vol. 31, No. 8, August 1939.

article by Fisher, paces 

1. THE PROCESS OF INCREASING THE PLASTICITY OF AN ELASTOPRENE OF THE CLASS CONSISTING OF NATURAL RUBBER AND THE POLYMERS OF 1,3-BUTADIENE AND OF 2-CHLORO-1,3-BUTADIENE WHICH CONTAIN AT LEAST 50% OF THE 1,3-BUTADIENE COMPOUND, WHICH COMPRISES INTIMATELY INCORPORATING IN SUCH MATERIAL IN THE UNVULCANIZED FORM FROM 0.1% TO 5.0% OF AN ANILIDE OF A BETA-KETO ACID OF THE FORMULA R-CO-CH2-CO-NHR'', WHEREIN R STANDS FOR A RADICAL OF THE GROUP CONSISTING OF PHENYL AND NAPHTHYL RADICALS AND ALKYL RADICALS OF FROM 1 TO 6 CARBON ATOMS, AND R'' STANDS FOR A RADICAL OF THE GROUP CONSISTING OF PHENYL AND NAPHTHYL RADICALS. 